Electron tube SG2S (СГ2C) is a soviet voltage regulator. Stabilized voltage in the operating current range: 75,5±5,5V. Operating current: 5-40mA. Filling: argon-neon. SG2S is direct replacement for the similar types OA3 and VR75/30 (technical parameters are close to identical, OA3 and VR75/30 do have another bulb shape). Service life guarantee: not less than 500 operating hours. Original enclosed datasheet is available for download. New in box tubes, directly from the factory packing. Made in the 60's.